Active-matrix display devices, such as liquid crystal display devices and organic Electro Luminescence (EL) display devices, and the like employ Thin Film Transistors (TFT) in their pixel circuits.
An example of the thin-film transistors includes: a substrate; a gate electrode on the substrate; a gate insulating film over the gate electrode; a semiconductor layer on the gate insulating film; and a source electrode and a drain electrode which are electrically connected to the semiconductor layer.
Semiconductor layers in thin-film transistors are often made of silicon. However, in recent years, organic materials are used for semiconductor layers to provide organic thin-film transistors. For example, Patent Literature 1 (PLT-1) discloses such a conventional organic thin-film transistor.
Here, the description is given for an example of a TFT included in a pixel circuit of a display device. FIG. 12A is a top view of a conventional organic thin-film transistor 80. FIG. 12B is a cross-sectional view of the conventional organic thin-film transistor 80 taken along line A-A′ of FIG. 11A.
As shown in FIG. 12B, the organic thin-film transistor 80 includes a substrate 801, a gate electrode line 802a, a first signal line layer 802b, a gate insulating film 803, a drain electrode 808, a source electrode line 809, a second signal line layer 810, bank layers 807 and 807, an organic semiconductor layer 811, a protection film 812, and a planarizing layer 813. In other words, the organic thin-film transistor 80 consists mainly of: a channel part 80A provided with a bottom-gate TFT; a storage capacitor part 80B; and a signal line crossing part 80C.
The channel part 80A is a bottom-gate TFT that includes the substrate 801, the gate electrode line 802a, the gate insulating film 803, the drain electrode 808, the source electrode line 809, the organic semiconductor layer 811 having circumference defined by the bank layers 807 and 807, and the protection film 812. The storage capacitor part 80B is a capacitor that includes the substrate 801, the gate electrode line 802a, the gate insulating film 803, and the source electrode line 809. The signal line crossing part 80C includes the first signal line layer 802b and the second signal line layer 810 which cross each other. There is the gate insulating film 803 between the first signal line layer 802ba and the second signal line layer 810.